Spindle drive, actuator assembly, and method for producing a spindle drive

ABSTRACT

A spindle drive for an actuator assembly of a vehicle brake is provided, with a spindle and a spindle nut mounted on the spindle, which forms an actuating carriage which can be displaced between a retracted and an extended position in order to apply a brake lining against a brake rotor. The spindle nut has a pressure-distributing element at an end of the spindle nut which is close to the brake lining, and a contact surface of the pressure-distributing element which faces away from the spindle is continuously or discontinuously annular. Furthermore, an actuator assembly with a spindle drive is provided. In addition, a method for producing a spindle drive is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to German Priority Application No.102021129963.2, filed Nov. 17, 2021, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a spindle drive for an actuator assembly of avehicle brake, in particular for an electromechanically actuated brake,and to an actuator assembly with a spindle drive and to a method forproducing a spindle drive.

BACKGROUND

Two friction linings can be applied to a brake rotor by an actuatingcarriage in order to actuate an electromechanical vehicle brake. Forthis purpose, the actuating carriage contacts the back plate of a brakelining.

However, an application force may occur only locally in the region ofthe contact surface between the actuating carriage and the back plate ofthe brake lining.

SUMMARY

The disclosure discusses an arrangement to achieve a qualitativelyuniform distribution of the application force between a brake lining andthe brake rotor.

As discussed herein, a spindle drive for a vehicle brake, with a spindleand a spindle nut mounted on the spindle, forms an actuating carriagethat can be displaced between a retracted and an extended position inorder to place a brake lining against a brake rotor. The spindle nut hasa pressure-distributing element at an end of the spindle nut which isdose to the brake lining, and a contact surface of thepressure-distributing element which faces away from the spindle iscontinuously or discontinuously annular.

By virtue of a continuously or discontinuously annular contact surface,the application force when the brake lining is applied to the brakerotor is transmitted to a brake lining less punctually than in the caseof a round circular surface. This is caused by the fact that the contactsurface is shifted away from a centre of the brake lining by the annularshape. The application force is thus distributed particularly uniformlyover the whole or almost the whole surface of the brake lining, as aresult of which a braking procedure can be particularly effective. Inaddition, the brake lining becomes worn uniformly, as a result of whichconsistent braking behaviour is ensured in the long term.

In particular, a distribution of pressure between the friction liningand the brake disc as occurs in the case of hydraulic dual-piston brakecalipers can be generated by the spindle drive according to thedisclosure.

The annular contact surface can be continuously or discontinuouslycircular, oval or elliptical when viewed from the front. As a result,the shape of the annular contact surface can be adapted to the size ofthe brake disc and to a desired pressure distribution.

According to an exemplary arrangement, the pressure-distributing elementhas a frustoconical projecting collar which ends at the contact surfaceand widens out from an axial end of the spindle nut to the brake lining.The circumference of the contact surface is consequently greater thanthe circumference of the spindle nut, as a result of which theapplication force is distributed over as large as possible an area withat the same time a compact structure of the spindle drive. Inparticular, the pressure-distributing element has the same diameter asthe spindle nut at its end connected to the spindle nut.

Starting from the axial end of the spindle nut, the cross-section of thecollar preferably merges from a circular cross-section into an oval orelliptical cross-section. As a result, if it is produced separately fromthe spindle nut, the pressure-distributing element can be connectedsimply to the spindle nut, When the pressure-distributing element andthe spindle nut are manufactured integrally, such a design is likewiseadvantageous for manufacturing reasons because there is a gradualtransition from the spindle nut to the pressure-distributing element.

The contact surface can have at least one depression, viewed in a sideview. In the region of the depression, the pressure-generating elementis not in contact with the back plate of the brake lining even when thebrake lining is applied such that a discontinuously annular contactsurface results by virtue of the depression. The distribution of theapplication force can consequently be influenced in a more targetedfashion.

In the case of an oval or elliptical contact surface, the depression isarranged in particular in the region of the co-vertices. As a result,the pressure-distributing element is in contact with the back plate ofthe brake lining in the region of the vertices. The contact surface isconsequently on average shifted as far away from a centre of the brakelining as is advantageous with respect to the distribution of theapplication force.

According to an exemplary arrangement, the contact surface runs at anangle to a friction surface of the brake lining, in particular whereintwo regions of the contact surface which are situated circumferentiallyopposite each other have opposite inclinations. The regions of thecontact surface which are situated opposite each other are preferablyinclined towards the centre. In particular, the contact surface isroof-shaped when viewed from the side. The elasticity of thepressure-distributing element is compensated by a contact surfaceinclined to the friction surface or by a region of the contact surfacewith an opposite inclination. As a result, when thepressure-distributing element is forced towards the back plate of abrake lining in order to apply the brake lining to a brake rotor, theinclined regions are deformed elastically by the resulting pressure insuch a way that the contact surface is oriented parallel to the brakelining or the angle at which the contact surface runs parallel to thebrake lining is reduced. The contact surface thus runs in an unstressedstate at an angle to the friction surface of the brake lining.

The pressure-distributing element is preferably made from metal andpress-fitted or welded to the spindle nut. The pressure-generatingelement can also merge integrally into the spindle nut. In the case oftwo-part manufacture, the pressure-distributing element has acylindrical centring extension which sits in a recess of the spindlenut.

The spindle drive is preferably supported on an axial bearing in thebrake caliper via the spindle, wherein the contact surface of the axialbearing with the spindle is a conical surface. As a result, the axialbearing is bevelled at its contact surface with the spindle. By virtueof the bevel, the axial bearing can absorb not only axial forces butalso a certain amount of transverse force.

The spindle drive is preferably a ball screw. In a ball screw, ballstransmit the force between the spindle and the spindle nut. By virtue ofthe rolling movement of the balls, friction and wear are reduced in aball screw.

According to an exemplary arrangement, at least one cut-out, which leadsto a thread of the spindle and which forms a mounting opening for theballs of the spindle drive, is present in a circumferential wall of thespindle nut. Simple mounting of the balls is consequently possible evenin the case of a spindle nut which is closed on one side.

The disclosure also discusses an actuator assembly for a vehicle brake,with a brake lining, a brake rotor and a spindle drive. Thepressure-distributing element is arranged at an end of the spindle nutwhich faces the brake lining and the contact surface of thepressure-distributing element is in contact with a back plate of thebrake lining in an extended position of the spindle nut and applies thebrake lining to the brake rotor. As has already been described inconnection with the spindle drive according to the disclosure, theapplication force is consequently distributed particularly uniformlyover the whole or almost the whole surface of the brake lining.

According to a method, in a first step, balls are inserted into a threadof the spindle, and in a following step the pressure-distributingelement is fastened to the spindle nut. In particular, thepressure-distributing element is press-fitted onto the spindle nut andis secured against rotation by a knurled joint or is welded. The ballscan be mounted as in a conventional ball screw by thepressure-distributing element being fastened to the spindle nut afterthe balls have been inserted into the thread. To be precise, the ballscan be mounted in the threads and ball returns of the spindle nut by acylindrical rod being pushed gradually into the latter. The balls aresecured against falling out by the cylindrical rod in the spindle nut.The spindle is then twisted into the spindle nut at one end of thelatter and the cylindrical rod is thus pushed out of the nut at theother end.

According to a further method, the pressure-distributing element ismanufactured as a single piece with the spindle nut, wherein at leastone cut-out, which leads to a thread of the spindle, is present in acircumferential wall of the spindle nut, and wherein the balls of thespindle drive are blown into the thread by compressed air through thecut-out. In this case, the advantage is obtained that thepressure-generating element does not need to be fastened subsequently tothe spindle.

The balls are arranged, for example, in a mounting tube which is pluggedinto the cut-out and to which compressed air is applied in order to blowthe balls into the thread.

BRIEF DESCRIPTION OF DRAWINGS

Further advantages and features of the disclosure emerge from thefollowing description and from the attached drawings to which referenceis made. In the drawings:

FIG. 1 shows an actuator assembly according to the disclosure for avehicle brake with a spindle drive according to the disclosure in a viewin section,

FIG. 2 shows a drive assembly of the actuator assembly from FIG. 1 ,

FIG. 3 shows the spindle drive from FIG. 1 in a perspective view,

FIG. 4 shows the spindle drive from FIG. 1 in a further perspectiveview,

FIG. 5 shows the spindle drive from FIG. 1 in a side view,

FIG. 6 shows the spindle drive from FIG. 1 with a brake lining in a sideview,

FIG. 7 shows a spindle drive according to the disclosure according to afurther exemplary arrangement in a perspective view,

FIG. 8 shows the spindle drive from FIG. 7 in a view in partial section,and

FIG. 9 shows a further spindle drive according to the disclosure in aperspective view.

DETAILED DESCRIPTION

FIG. 1 shows an actuator assembly 10 as part of an electromechanicalvehicle brake.

The actuator assembly 10 comprises a control assembly 12 which can bemounted as a separate subunit, and a drive assembly 14 which can bemounted as a separate subunit (see FIG. 2 ).

The control assembly 12 and the drive assembly 14 are arranged in acommon housing 16.

The housing 16 comprises an essentially sleeve-shaped housing base part18 and a housing cover 20 by which the housing base part 18 is tightlyclosed in the mounted state.

In the exemplary arrangement illustrated, the housing cover 20 is alsoessentially shell-shaped.

Both the housing base part 18 and the housing cover 20 are produced fromplastic material. The housing 16 as a whole is thus made from plasticmaterial.

The actuator assembly 10 furthermore comprises a brake caliper 15 inwhich a gap 17 is formed for a brake rotor 19, i.e. a brake disc. Thehousing 16 is pushed partially onto the brake caliper 15 with its endclose to the brake caliper 15.

The drive assembly 14 comprises a support assembly 22 which has aplate-like frame part 24, as can be seen particularly well in FIG. 2 .

A first fastening interface 26, at which an electric motor 28 isfastened in the exemplary arrangement illustrated, is provided on theplate-like frame part 24.

To be more precise, the electric motor 28 is connected captively to theframe part 24 via the first fastening interface 26. The frame part 24absorbs the forces of the electric motor 28 and holds the latter.

The electric motor 28 fastened to the frame part 24 such that is centredwith respect to a centre axis 34 of the first fastening interface 26.

In addition, an anti-rotation device 36 is provided in the form of ananti-rotation depression which is designed to prevent the electric motor28 from rotating relative to the frame part 24.

An output gear wheel 40 is arranged on an output shaft 38 of theelectric motor 28, as shown in FIG. 2 , in order to impart torque to thedrive assembly 14.

Furthermore, a journal 42, on which in the exemplary arrangementillustrated a gear wheel 44 is mounted which meshes with the output gearwheel 40, is provided on the frame part 24.

Moreover, a receiving space 46 for a planetary gear stage 48 is providedon the frame part 24.

A centre axis 50 of the receiving space 46 is here arranged essentiallyparallel to the centre axis 34 of the first fastening interface 26.

A reinforcing part 52 is moreover fastened on the frame part 24 in sucha way that it spans the end of the receiving space 46 axially withrespect to the centre axis 50.

In the exemplary arrangement illustrated, the reinforcing part 52 isessentially cross-shaped.

In addition, a bearing point 54 for a gear wheel 56 arranged coaxiallywith respect to the planetary gear stage is provided on the reinforcingpart 52.

The gear wheel 56 meshes with the gear wheel 44.

A gear train 58 is consequently formed by the gear wheel 44 and the gearwheel 56, the output gear wheel 40 acting as its input member.

The gear wheel 56 is moreover formed integrally with a sun gear 60 (seeFIG. 1 ) of the planetary gear stage 48. In this way, the gear train 58and the planetary gear stage 48 are coupled drivingly.

The planetary gear stage 48 moreover comprises a ring gear 62 which runsessentially along an inner circumference of the receiving space 46 (seeFIG. 1 ).

In the exemplary arrangement illustrated, a total of three planetarygears 64 are provided drivingly between the sun gear 60 and the ringgear 62, as can be seen in FIG. 2 . They are mounted rotatably on aplanet carrier 66.

The planet carrier 66 here represents an output element of the planetarygear stage 48.

The gear train 58 and the planetary gear stage 48 are also referred totogether as a gear unit 67.

The frame part 24 furthermore has a second fastening interface 68 whichis designed for fastening a guide part 70, held therein, for a spindledrive 72.

In the exemplary arrangement, the guide part 70 is a bearing sleevewhich is held in the brake caliper 15. For example, the bearing sleeveis press-fitted in the brake caliper or is welded to the latter.

A centre axis of the second fastening interface 68 here coincides withthe centre axis 50 of the receiving space 46 and for this reason isprovided with the same reference numeral.

The second fastening interface 68 has an anti-rotation geometry 74, forexample a splined shaft geometry, which runs circumferentially aroundthe centre axis 50.

A complementary anti-rotation geometry 82 is provided at that end of theguide part 70 which is to be coupled to the second fastening interface68 such that the guide part 70 can be pushed along the centre axis 50into the anti-rotation geometry 74 of the second fastening interface 68and held there non-rotatably in a form-fitting fashion. Theanti-rotation geometry is likewise a splined shaft geometry.

The spindle drive 72 is accommodated inside the guide part 70.

It comprises a spindle 84 which is configured in the present case as aball screw.

The spindle 84 is here connected non-rotatably to the planet carrier 66via the toothed section 86.

The spindle drive 72 can thus be driven by the electric motor 28. Indetail, the electric motor 28 is coupled to the spindle drive 72drivingly via the gear train 58 and the planetary gear stage 48.

A spindle nut 88, which is configured as a piston and forms an actuatingcarriage for a brake lining, is mounted on the spindle 84.

Rotation of the spindle 84 thus causes the spindle nut 88 to be shiftedaxially along the centre axis 50.

The spindle nut 88 is here guided along the centre axis 50 directly on arunning surface 90, wherein the running surface 90 is formed by an innerside of the guide part 70. The running surface 90 correspondsessentially to a cylindrical surface forming the inner circumference ofthe guide part 70. In other words, the spindle nut 88 is guided linearlydisplaceably in the guide part 70.

The guide part 70 is open towards the gap 17 such that the spindle nut88 can move into the gap 17.

The spindle nut 88 is moreover prevented from rotating relatively aboutthe centre axis 50 by an anti-rotation device 92 which is designed as aslot on the guide part 70. For this purpose, an anti-rotation element 94which engages in the slot (see FIG. 1 ) is attached to the spindle nut88. In the exemplary arrangement, the anti-rotation element 94 is aradial extension.

The spindle nut 88 serves to apply a first brake lining 96 of a brakecaliper assembly 98 to the brake rotor 19. As a result, the first brakelining 96 can be moved actively onto a brake rotor 19 by the actuatorassembly 10.

In detail, the spindle nut 88 is transferred selectively into anextended position, which is associated with the application of the firstbrake lining 96 to the brake rotor 19, by the electric motor 28 via thegear train 58, the planetary gear stage 48 and the spindle drive 72.

Because of the reaction forces acting inside the actuator assembly 10and the brake caliper assembly 98, a second brake lining 102 isconsequently also applied to the brake rotor 19.

It should be understood that the spindle nut 88 can be moved in the sameway by operation of the electric motor 28 into a retracted positionwhich is associated with lifting the first brake lining 96 and thesecond brake lining 102 off the brake rotor 19.

The spindle drive 72 is supported on an axial bearing 104 in the brakecaliper 15 via the spindle 84.

Specifically, in the exemplary arrangement, the axial bearing 104 issupported on a wall 105 which is formed integrally with the guide part70 and which runs transversely to a direction of movement of the spindlenut 88. In the exemplary arrangement, the wall 105 is a radially inwardfacing flange.

A contact surface 106, which is in contact with the spindle 84, of theaxial bearing 104 is a conical surface. As a result, transverse forces,which occur in particular when the brake lining 96 is applied to thebrake rotor 19, can be absorbed by the axial bearing 104 and be absorbedby the brake caliper 15 via the guide part 70.

The axial bearing 104 is a rolling bearing, in particular a needlebearing.

In the present case, the actuator assembly 10 is designed so that it isnot self-locking, such that the spindle nut 88 also shifts backautomatically into the retracted position by virtue of elasticitiesinherent in the system when it is no longer actively forced into theextended position by the electric motor 28.

A spindle drive according to a first arrangement will be described belowin detail with the aid of FIGS. 3 to 6 , in particular the spindle drive72 of the actuator assembly 10 shown in FIG. 1 .

The spindle nut 88 has a pressure-distributing element 108 at an end ofthe spindle nut 88 which is close to the brake lining 96.

The pressure-distributing element 108 is, for example, made from metal.

In the exemplary arrangement, the pressure-distributing element 108 ismanufactured separately from the spindle nut 88 and press-fitted orwelded to the spindle nut 88. In this case, the pressure-distributingelement 108 preferably has a cylindrical centring extension 110 whichsits in a recess 112 of the spindle nut 88 (see FIG. 1 ).

In the case of two-part manufacture, the pressure-distributing element108 forms a sealing cap for the spindle nut 88.

The pressure-distributing element 108 can also merge into the spindlenut 88 as a single piece. The spindle nut 88 with the integratedpressure-distributing element 108 can be produced in this case as amilled or cast part.

A contact surface 114, facing away from the spindle 84, of thepressure-distributing element 108 is annular (see FIG. 4 ). To be moreprecise, the annular contact surface 114 is oval when viewed from thefront. An elliptical or circular contact surface 114, designed as aring, is, however, also conceivable.

In an extended position of the spindle nut 88, the contact surface 114of the pressure-distributing element 108 is in contact with a back plate115 (see FIG. 6 ) of the brake lining 96 and applies the brake lining 96to the brake rotor 19.

In the arrangement according to FIGS. 3 to 6 , the contact surface 114is in particular discontinuously annular, which is explained in moredetail below.

The pressure-distributing element 108 has a frustoconical projectingcollar 116.

Starting from an axial end of the spindle nut 88, the collar 116 widensout towards the brake lining 96 and ends at the contact surface 114. Thecontact surface 114 consequently has a larger external circumferencethan the spindle nut 88, in particular an external circumference whichis larger by at least 50%.

In the exemplary arrangement, starting from the axial end of the spindlenut 88, the cross-section of the collar 116 merges from a circularcross-section into an oval cross-section.

As can be seen particularly well in FIG. 1 , the collar 116 has, at theend fastened to the spindle nut 88, the same diameter as the spindle nut88. To be more precise, a diameter of the collar 116 at its base is thesame size as an average diameter of the spindle nut 88 or as a diameterat a circumferential surface of the recess 112. The circumference of thecontact surface 114 is consequently greater than the circumference ofthe spindle nut 88.

There is a clearance between the collar 116 and an end side of thespindle nut 88 such that a circumferential depression 118 is formed forreceiving a seal 120. Such a clearance can be obtained simply by anappropriate dimensioning of the recess 112.

The depression 18 is formed in particular when the pressure-distributingelement 108 is attached to the spindle nut 88.

As can be seen in FIGS. 5 and 6 , which each show the spindle drive 72in a side view, the contact surface 114 has two depressions 122 whenviewed from the side.

The discontinuously annular form of the contact surface 114 which hasalready been mentioned above is obtained by the depressions 122. Thereis in particular no contact of the pressure-distributing element 108with the back plate 115 of the brake lining 96 in the region of thedepressions 122. The contact surface 114 thus comprises two ringsegments 124.

In the case of an oval or elliptical contact surface 114, the depression122 is arranged in the region of the co-vertices 125. The contactsurface 114 is thus in contact with the back plate 115 of the brakelining 96 in the region of the vertices 126.

As can be seen in FIG. 5 , the ring segments 124 of the contact surface114 run at an angle a to a friction surface 117 of the brake lining 96.In particular, two regions of the contact surface 114 which are situatedopposite each other at the circumference, to be more precise the tworing segments 124 formed by the depressions 122, have oppositeinclinations. Specifically, the ring segments 124 are inclined towardsthe centre of the pressure-distributing element 108 such that thecontact surface 114 is roof-shaped when viewed from the side.

Because a pressure-distributing element 108 is provided on the spindlenut 88, improved distribution of the application force in the brakelining is achieved such that the brake lining 96 is deformed as littleas possible when acted upon by the spindle nut 88 or thepressure-distributing element 108 and is consequently applied to a largearea of a brake disc of the brake rotor 19.

A further spindle drive 72 according to the disclosure, which canlikewise be used in the actuator assembly 10 shown in FIG. 1 , isillustrated in FIGS. 7 to 8 .

The same reference numerals are used below for the same structures withthe same functions which are known from the above arrangement andreference is made in this respect to the preceding explanations, whereinthe differences in the respective arrangements are discussed below inorder to prevent repetitions.

In the arrangement of the spindle drive 72 illustrated in FIGS. 7 to 8 ,the contact surface 114 is not oval and instead is circular. Moreover,there are no depressions 122.

In particular, the contact surface 114 is flat in FIGS. 7 to 8 .

The spindle drive 72 illustrated in FIGS. 7 to 8 is suited in particularfor combination with smaller brake linings than the spindle drive 72illustrated in FIGS. 1 to 6 .

FIG. 9 shows a further spindle drive 72 according to the disclosure.

The spindle drive 72 illustrated in FIG. 9 differs from the spindledrive illustrated in FIGS. 7 and 8 in that at least one cut-out 130,which leads to a thread 132 of the spindle 84, is present in acircumferential wall 128 of the spindle nut 88.

The cut-out 130 forms in particular a mounting opening for the balls 134of the spindle drive 72.

The spindle drive 72 according to FIGS. 3 to 6 and 7 to 8 can optionallylikewise have a cut-out 130 in the circumferential wall 128 of thespindle nut 88.

The cut-out 130 enables mounting of the spindle drive 72 when thepressure-distributing element 108 forms a single piece with the spindlenut 88 or when the pressure-distributing element 108 has been connectedto the spindle nut 88 before the spindle nut 88 is mounted on thespindle 84.

The balls 134 of the spindle drive 72 can be blown through the cut-out130 into the thread 132 by compressed air.

The balls 134 are, for example, arranged in a mounting tube 136 which ispushed into the cut-out and to which compressed air is applied in orderto blow the balls into the thread. The mounting tube 136 preferably hasa curve.

The ball return can be integrated into the spindle nut 88 or into thespindle 84.

For example, a ball return integrated into the spindle 84 is providedwith individual ball recirculation functionality. In this case, acut-out 130 is provided as a mounting opening for each individual ballrecirculation.

The cut-outs 130 can be closed with a cover once the mounting iscomplete.

In a first step the balls 134 can also be inserted into the thread 132of the spindle 84, and in a subsequent step the pressure-distributingelement 108 is fastened to the spindle nut 88, In this case, a rod,which serves as a mounting aid, can be pushed gradually into the spindlenut 88, wherein the balls 134 are mounted in the threads of the spindlenut 88. The balls 134 are secured against falling out during mounting byvirtue of being covered by the cylindrical rod. The spindle 84 can thenbe screwed into the spindle nut 88, wherein the rod is pushed out of thespindle nut 88. Afterwards, the pressure-distributing element 108 can befastened to the spindle nut 88.

Regardless of whether the pressure-distributing element 108 is fastenedto the spindle nut 88 before or after the balls 134 are mounted, thepressure-distributing element 108 can be press-fitted to the spindle nut88 and secured against rotation by a knurled joint. Thepressure-distributing element 108 can also be welded to the spindle nut88.

1. A spindle drive for an actuator assembly of a vehicle brake, thespindle drive including a spindle and a spindle nut mounted on thespindle that forms an actuating carriage that can be displaced between aretracted and an extended position in order to apply a brake liningagainst a brake rotor, wherein the spindle nut has apressure-distributing element at an end of the spindle nut that is closeto the brake lining, and wherein a contact surface of thepressure-distributing element that faces away from the spindle iscontinuously or discontinuously annular.
 2. The spindle drive accordingto claim 1, wherein the annular contact surface is at least one ofcontinuously or discontinuously circular, oval, or elliptical whenviewed from the front.
 3. The spindle drive according to claim 1,wherein the pressure-distributing element has a frustoconical projectingcollar that ends at the contact surface and widens out from an axial endof the spindle nut to the brake lining.
 4. The spindle drive accordingto claim 3, wherein, starting from the axial end of the spindle nut, thecross-section of the collar merges from a circular cross-section into anoval or elliptical cross-section.
 5. The spindle drive according toclaim 1, wherein the contact surface has at least one depression, viewedin a side view.
 6. The spindle drive according to claim 5, wherein, inthe case of an oval or elliptical contact surface, the depression isarranged in the region of the co-vertices.
 7. The spindle driveaccording to claim 1, wherein the contact surface runs at an angle to afriction surface of the brake lining, wherein two regions of the contactsurface that are situated circumferentially opposite each other haveopposite inclinations.
 8. The spindle drive according to claim 1,wherein the pressure-distributing element is made from metal andpress-fitted or welded to the spindle nut, or in that thepressure-distributing element merges into the spindle nut as a singlepiece.
 9. The spindle drive according to claim 1, wherein the spindledrive is supported on an axial bearing in the brake caliper via thespindle, wherein the contact surface of the axial bearing with thespindle is a conical surface.
 10. The spindle drive according to claim1, wherein the spindle drive is a ball screw.
 11. The spindle driveaccording to claim 1, wherein at least one cut-out, which leads to athread of the spindle and which forms a mounting opening for the ballsof the spindle drive, is present in a circumferential wall of thespindle nut. 12.-14. (canceled)
 15. An actuator assembly for a vehiclebrake, the actuator assembly including: a brake lining, a brake rotor,and a spindle drive, the spindle drive including with a spindle and aspindle nut mounted on the spindle that forms an actuating carriage thatcan be displaced between a retracted and an extended position in orderto apply a brake lining against a brake rotor, wherein the spindle nuthas a pressure-distributing element at an end of the spindle nut that isclose to the brake lining, wherein a contact surface of thepressure-distributing element that faces away from the spindle iscontinuously or discontinuously annular, wherein thepressure-distributing element is arranged at an end of the spindle nutthat faces the brake lining and the contact surface of thepressure-distributing element is in contact with a back plate of thebrake lining in an extended position of the spindle nut and applies thebrake lining to the brake rotor.
 16. The actuator assembly according toclaim 15, wherein the annular contact surface is at least one ofcontinuously or discontinuously circular, oval, or elliptical whenviewed from the front.
 17. The actuator assembly according to claim 15,wherein the pressure-distributing element has a frustoconical projectingcollar that ends at the contact surface and widens out from an axial endof the spindle nut to the brake lining.
 18. The actuator assemblyaccording to claim 17, wherein, starting from the axial end of thespindle nut, the cross-section of the collar merges from a circularcross-section into an oval or elliptical cross-section.
 19. The actuatorassembly according to claim 15, wherein the contact surface has at leastone depression, viewed in a side view.
 20. The actuator assemblyaccording to claim 15, wherein the contact surface runs at an angle to afriction surface of the brake lining, wherein two regions of the contactsurface that are situated circumferentially opposite each other haveopposite inclinations.